1. Field of Invention
The present invention relates to a method for supporting mode walls, or other wall-like structures, without the use of conventional attachment methods such as screws or clips.
2. Description of the Related Art
Mode walls are thin wall structures typically used within electronic equipment for a variety of purposes, including isolating electrical components from electromagnetic interference (EMI) emissions. Mode walls are necessarily widely used in a variety of electrical devices such as audio amplifiers, cellular phones, and others.
FIG. 1 shows a conventional method of supporting a mode wall structure within an environment of amplifier pallets. A mode wall 11 having an L-shaped feature 13 is positioned in a slot 16 between two amplifier pallets 10. The mode wall 11 is supported by using a screw 14, which secures the mode wall 11 onto a bed of substrate 12 by connecting the L-shaped feature 13 to the substrate 12. The substrate 12 has a cavity 15 that is wide enough to allow for insertion of the L-shaped feature 13. The L-shaped feature 13 and the cavity 15 must also be sufficiently wide to allow for insertion of an attaching mechanism such as a screw 14 and tools required to fix the attaching mechanism in place.
Many disadvantages are associated with the conventional method illustrated in FIG. 1. First, due to the compact arrangements of components typically found within electrical circuitry, it is often very difficult to insert a device such as a screw gun to secure the L-shaped feature 13 within the cavity 15. At the same time, it often becomes very difficult to insert a mode wall with an L-shaped feature into a slot that is, in the case of amplifier circuits, often no wider than 0.03 inches. Furthermore, because a cavity must be formed to support an L-shaped feature, at least part of one of the amplifier pallets 10 extends over empty space. Incidentally, surface contact with the underlying substrate material allows an amplifier pallet to disperse excess thermal energy, a process that is essential in achieving maximum power capability. Consequently, reduced surface contact with the substrate below, as in the case of a cavity formation, decreases an amplifier pallet""s power capability.
FIG. 7 shows another example of a conventional method of supporting mode wall-like structures. Small metal clips 73 are installed at several locations on a circuit board 72 using either hand mounting techniques or surface mount technology. The mode wall 71 is then installed between the metal clips 73. The location and the number of metal clips 73 determines the grounding points for the mode wall 71 and therefore its relative effectiveness. Several disadvantages are associated with this conventional method of support. First, it can be costly to manufacture and install the metal clips 73. More particularly, it may become very difficult and time consuming to access through the neighboring components on the circuit board in order to align accurately each metal clip such that the metal clips 73 form an accurate linear path or a path matching the curvature of the mode-wall like structure to be installed. Second, it may become difficult to install the mode wall-like structure in between the clips, especially if the mode-wall like structure is not linear. Finally, a mode-wall installed using metal clips may not be appropriately grounded through limited contact using the clips.
FIG. 2 shows another example of a conventional method for supporting mode wall-like structures. A thin elongated slot 22 is cut on a substrate 20 using a diameter cutter. The diameter of the thin slot 22 is slightly larger than the width of the mode wall 21 such that mode wall 21 can fit snugly and rigidly into the thin slot 22. The mode wall 21 is grounded in several portions at which the mode wall 21 comes in contact with electrical contacts 23, which are tightly pressed between the outer side of mode wall 21 and an inner side of the thin slot 22.
The method illustrated in FIG. 2 also causes many disadvantages and difficulties. First, there is a limit on how thin a slot can be cut by a diameter cutter. Currently, the thinnest slot width able to be cut by a diameter cutter is about {fraction (1/32)} of an inch in width (approximately 0.03 inches). This minimum width requires the use of heavier sheet metals in order to accommodate a snug fit. In addition, a small diameter cutter has a significant deflection problem, which makes it difficult to meet and satisfy tight tolerances at any reasonable metal removal rates. Moreover, due to the deflection problem, small diameter cutters are often manufactured with a short overall length to minimize the deflection. Since the body of a diameter cutter is generally much wider than the cutter itself, this limits the cutter""s ability to access tight spaces on the substrate within an amplifier case (a problem otherwise known as milling head interference). Finally, if a slot with interference is required, the full length of the slot must be an interference or snug fit, making it difficult to install a thin mode wall into the slot. An interference fit of this type often requires that the application of load from both sides of the slot to xe2x80x9ccrushxe2x80x9d the mode wall in order for the mode wall to be properly secured. As a result, elements such as electrical contacts 23 from FIG. 2 become extremely difficult to assemble.
The present invention overcomes the disadvantages associated with conventional wall support methods by providing a method of supporting mode walls, or other wall-like structures, without the use of conventional attachment mechanisms such as screws or clips, and without the requirement of using small diameter cutters with high milling head interference.
A preferred embodiment of the present invention provides a method which uses a medium to large diameter cutter to cut a serpentine path having a substantially straight centerline. The width of the serpentine slot and distance of the slot walls from the centerline is constructed such that an area of center clearance is produced by the cutting action. The area of center clearance produced is capable of supporting a wall-like structure having a width that is significantly narrower than that of the serpentine slot width.
One advantage of preferred embodiments of the present invention includes the ability to provide support to mode walls or wall-like structures without the use of small diameter cutters. The method according to a preferred embodiment of the present invention allows the use of a medium to large sized diameter cutter that is made of a more rigid structure, allowing greater cutting rates and the ability to meet and maintain tighter tolerances at such higher cutting rates.
Another advantage of the present invention includes the ability to support very thin mode wall structures that would not be possible or at least very difficult to support using conventional support methods. In particular, because the cutting of a serpentine path produces a central clearance having a width that is much narrower than the width of the serpentine slot itself, the serpentine slot is capable of supporting a very thin wall structure.
Another advantage of the present invention includes maximizing the amplifier power of an amplifier in an environment where the mode walls are supported between amplifier pallets. Specifically, because the preferred embodiments of the present invention abbreviates the formation of cavities underneath amplifier pallets to support an L-shaped feature, preferred embodiments of the present invention achieve greater thermal contact between the substrate and the amplifier pallet. This results in greater thermal capability for the amplifier pallet and therefore a greater power rating capability for the amplifier pallet.
Another advantage of the present invention includes providing the ability to ensure grounding of the mode wall or thin structure at predetermined locations or spacings as may be required. More particularly, the mode wall according to an embodiment of the present invention can be grounded at particular points of contact with the inner sides of the serpentine slot. By manipulating the numbers of curves per distance on the serpentine slot, the spacings between points or ground contacts can be accurately controlled. To allow guaranteed ground contacts at selected points, shortening the ground return distance for EMI and guaranteeing that particular spurious modes are grounded out.
Another advantage of the present invention includes providing the ability to easily manufacture boards or substrates having serpentine slots to support thin mode walls. An alternative to creating a slot other than by using a diameter cutter is to manufacture a substrate using a die cast method. When creating a slot using the die cast method, the mold includes a thin protrusion that can be used to cast a thin slot. In the case of a thin straight slot, it is often difficult to create a mold having a thin protrusion that is sturdy enough to be used to cast a thin slot. According to one preferred embodiment of the present invention, a thicker serpentine protrusion can be used to cast a thicker serpentine slot, while still supporting a thin mode wall structure.